Differential roles for Bak in Triton X-100-and deoxycholate-induced apoptosis

We recently reported that Bax activation occurs downstream of caspase activation in Triton X-100 (TX)induced apoptosis. Here, Bak was found to be activated in TX-induced apoptosis. Although z-VAD-fmk completely Suppressed Bax activation, it only partially attenuated TX-induced Bak activation. Moreover, activation of both Bak and Bax was detected in apoptosis induced by deoxycholate, a physiological detergent in bile. z-VAD-fmk completely Suppressed deoxycholate-induced Bak as well as Bax activation. Furthermore, Bak siRNA attenuated TV but not deoxycholate-induced caspase activation. These results Suggest that Bak activation May Occur upstream of caspase activation in TX- but not deoxycholate-induced apoptosis and that the mechanism of TX-induced apoptosis may differ from that of deoxycholate-induced apoptosis at least with regard to the role for Bak. (C) 2008 Elsevier Inc. All rights reserved.